This invention relates to magnetic tape cassettes such as digital video cassette (DVC), tape reels for use with them that can be broken down into parts, resinous (plastic) leaf springs, and a process for producing them.
More specifically, the invention relates to a magnetic tape cassette that has magnetic tape housed in a case made by joining an upper and a lower half in a face-to-face relationship and which can be disposed of by assorting the constituent materials simply enough to reduce the impact on the environment, thereby facilitating the recycling of the used cassette.
In order to ensure that the magnetic tape cassette discarded after use is broken down into various parts which are then assorted by material and recycled as feedstock for a second production, the invention also provides tape reels in a magnetic tape cassette which are of such a structure that the lower flange can be easily separated from the upper flange, the two flanges capable of being securely joined together at high enough precision in assembly to minimize wobbling of the upper flange.
The invention also relates to resinous (plastic) leaf springs that can be molded while achieving proper adjustment of spring load, as well as a process for producing such leaf springs.
Recording media cartridges and cassettes conventionally used as the recording media in external storages in computers and the like are divided into two major classes, magnetic or magneto-optical disk cartridges, etc. that use disks such as magnetic disks or magneto-optical disks as the recording media, and magnetic tape cartridges or cassettes, etc. that use magnetic tape as the recording media (and which are hereunder collectively referred to as “magnetic tape cassettes”).
The magnetic or magneto-optical disk cartridges and the magnetic tape cassettes are also used to record and store data from computers and the like. In order to protect the stored valuable or important information, design consideration is made such that magnetic or magneto-optical disks will not be damaged or that magnetic tape will not jam or receive damage or will not be pulled accidentally out of the record/reproduce apparatus.
The magnetic tape cassettes of the second class are used as record/reproduce media in consumer or professional sound or image recording/reproducing apparatus (including various types of recorders such as video tape recorder and video cameras) or as large-capacity recording media to back up data in external storages in computers and the like.
Such magnetic tape cassettes are available in two types, the first type comprising magnetic tape stretched between a pair of tape reels that are housed rotatably within a case (body case) composed of an upper and a lower half (this is a so-called two-reel type) and the second type comprising magnetic tape wound around a single tape reel which is also housed rotatably in the case (this is a so-called one-reel type). Known examples of such magnetic tape cassettes include those whose structural and dimensional specifications are described in JIS X6127, X6129, X6130, X6171 and X6172, as well as in ECMA-288, etc.
On the pages that follow, a magnetic tape cassette of a two-reel type is described specifically as an example of the magnetic tape cassette. Intended typically for use as a digital video cassette (DVC), it consists of a case that contains a pair of tape reels around which magnetic tape is wound and which allow the magnetic tape to run for information recording and reproduction.
FIG. 53 is an exploded perspective view showing the structure of the prior art two-reel type magnetic tape cassette. As shown, the case of the magnetic tape cassette which is generally indicated by 450 consists of an upper half 452 and a lower half 454 that each have a rectangular bottom plate and peripheral walls and which are joined in a face-to-face relationship and secured by a plurality of fasteners such as screws 455 (which are five in the illustrated case).
In the interior of the case 450 which is composed of the upper half 452 and the lower half 454, magnetic tape 458 which is stretched between a pair of tape reels 456, one on the supply side and the other on the take-up side, is rotatably housed. Various other parts are also housed in the interior of the case 450. The pair of tape reels 456 are positioned along a sidewall 454c of the lower half 454 and their movement in a plane is regulated by, for example, a plurality of ribs 454e erected on the bottom plate 454a of the lower half 454. Each of the tape reels 456 consists of a reel hub (take-up hub) 456b to which an upper flange 456c and a lower flange 456d are both welded.
The bottom plate 454a of the lower half 454 has two extensions 460 that extend from the right and left sides in a forward direction (to the left in FIG. 53). The extensions 460 have semi-cylindrical tape guides 464 that stand vertically on the bottom plate 454a and by which the magnetic tape 458 stretched between the tape reels 456 is allowed to thread through a predetermined path to become exposed in an opening 462 at the front face of the cassette case. The space between the extensions 460 is not occupied by the lower half 454 but forms the opening 462 in the cassette case.
The bottom plate 454a of the lower half 454 also has two reel shaft insertion holes 454b. By means of the insertion holes 454b, a pair of tape reels 456 between which the magnetic tape 458 is stretched are supported rotatably and, in addition, when the magnetic tape cassette is loaded on the record/reproduce apparatus, reel shafts (not shown) on the record/reproduce apparatus pass through insertion holes (not shown) in the lower side of the tape reels 456 to engage them and thereby drive them to rotate.
The bottom plate 452a of the upper half 452 has openings so that the amount in which the magnetic tape 458 has been wound around the tape reels 456 can be seen (checked visually) from the outside of the case 450. In the openings, transparent window members (inspection windows) 452b made of transparent plastic (resin) are mounted by a suitable method such as ultrasonic or thermal welding.
A pair of reel retaining springs 466 in the form of a metallic leaf-like reel urging spring are provided on the inner surface of the upper half 452 (the lower surface in FIG. 53) in positions that correspond to the respective tape reels 456. Each of the reel retaining springs 466 is a leaf spring; its distal end portion 466a is bent downwardly and its basal end portion 466b is fastened to the lower surface of the bottom plate 452a of the upper half 452 (its inner surface) by a suitable means such as screwing, ultrasonic welding or thermal welding (neither is shown) so that the distal end portion 466a is cantilevered and depresses the center of the corresponding tape reel 456 to be urged toward the lower half 454.
In order to ensure that dust will not get into the upper half 452 when the magnetic tape cassette is not in service, the front face of the upper half 452 (the left lateral face in FIG. 53) is fitted with a front cover (lid) 467 which covers and protects the magnetic tape 458 (its front and back sides) as it is stretched between a pair of tape guides 464 on the lower half 454. The front cover (lid) 467 consists of three members, an outer lid 468, an upper lid 470 and an inner lid 472. The outer lid 468 has lock pins (guide pins) 474 that project inwardly from both lateral plates 468a. Since the lock pins 474 fit into engage-and-stop grooves 452d in two sidewalls 452c of the upper half 452, the whole of the front cover 467 can rotate to open in a direction approaching the upper surface of the upper half 452. On the other hand, torsion coil springs 475 fitted on the lock pins 474 urge the lid 467 in such a direction that it closes the opening 462 between the two extensions 460 of the bottom plate 454a of the lower half 454 of the magnetic tape cassette.
Sidewall portions 454c of the lower half 454 are fitted with rotatable lid locking members 476 that engage the lock pins 474 on the outer lid 468 to keep it closed. The lid locking members 476 are urged to engage the lock pins 474 by means of lid locking springs (not shown) which are similarly mounted on the lower half 454.
When the magnetic tape cassette is taken out of the record/reproduce apparatus, the lid locking members 476 keep the outer lid 468 closed so that the operator will not inadvertently touch the magnetic tape 458. When the magnetic tape cassette is reloaded into the record/reproduce apparatus, the engagement is removed by release pins (not shown) that project from the record/reproduce apparatus, whereupon the outer lid 468 can be rotated to open.
The lower half 454 also has a tape reel locking member 478 mounted in the rear end portion (the right farther end in FIG. 53). The tape reel locking member 478 has tape reel engage-and-stop arms 478a and a slidable body 478b. The slidable body 478b is slidably held by a pair of guide ribs 454d erected on the bottom plate 454a of the lower half 454 and it is urged forward by a compressive coil spring 480; as a result, each of the tape reel engage-and-stop arms 478a that spread in a V-shape come into engagement at the distal end with engaging teeth 456a formed on the circumference of the lower flange of the corresponding tape reel 456, thereby preventing it from rotating to ensure that the magnetic tape 458 will not unwind accidentally to get slack.
The lower half 454 is also fitted with an anti-erasure plug 482 that prevents inadvertent erasure of the data recorded on the magnetic tape 458. The anti-erasure plug 482 has a finger that projects from a lateral surface (the farthest side in FIG. 53) to become exposed to the outside through an opening in a peripheral wall of the upper half 452. By external manipulation of the finger, the anti-erasure plug 482 can be moved back and forth along a guide rib erected on the bottom plate 454a of the lower half 454, thereby closing or opening a detection hole in the bottom plate 454a of the lower half 454. A machine such as the record/reproduce apparatus reads the state of the detection hole and, depending on whether it is open or closed, determines whether new data can be written to the magnetic tape 458.
The upper half 452, the lower half 454, the front cover 467 (i.e., the outer lid 468, the upper lid 470 and the inner lid 472) and other principal components of the magnetic tape cassette are formed of the same resin (plastic) material by injection molding. The tape reels 456 (each consisting of the reel hub 456b, the upper flange 456c and the lower flange 456d), the tape reel locking member 478 and other members are formed of a different plastic material by injection molding. The magnetic tape cassette may of course use other injection molded members as appropriate.
As already mentioned, the conventional magnetic tape cassette uses the reel retaining springs 466 that keep the tape reels 456 from rotating in order to ensure that the magnetic tape 458 will not get slack or otherwise deteriorate. The reel retaining springs 466 are metallic reel urging springs.
As shown in FIG. 53, such metallic reel urging springs are commonly a pair of reel retaining springs 466 that correspond to the pair of reels 456. Of course, various other designs of reel retaining spring have been used or proposed.
FIG. 54 shows another conventional method that is commonly used to hold the pair of reels 456; as shown, the reels are retained by means of a single reel retaining spring 486.
FIG. 54 is a perspective view showing the inside of the upper half fitted with a reel retaining spring of a different design than is shown in FIG. 53. The reel retaining spring 486 of the design shown in FIG. 54 has two end portions 486a bent downward, with the center portion 486b being fixed to the lower surface of the bottom plate 452a of the upper half 452 by a suitable method such as screwing, ultrasonic welding or thermal welding; both end portions 486a of the reel retaining spring 486 depress the tape reels 456 at the center so that they are urged toward the lower half 454 (see FIG. 53). The two end portions 486a of the reel retaining spring 486 are each cantilevered by means of the center portion 486b and this parallels with the reel retaining springs 466 shown in FIG. 53.
JP 60-166879 U discloses a reel retaining spring which is a mesa-shaped leaf spring and indicated by 488 in FIGS. 55A and 55B. The leaf spring 488 is provided for each of tape reels 490 and it has a center portion 488a and two end portions 488b and 488c; the center portion 488a will contact a pivot (convex) 490b on the top of the center reel hub 490a of each tape reel 490 and depresses and urges it toward the lower half 492, and the two end portions 488b and 488c are bent down toward opposite sides of the center portion 488a to fit into grooves 496 made in the inner surface of the upper half 494. The end portion 488b has a larger width at the distal end that fits into a corresponding wider portion 496a of the groove 496. In order to load the magnetic tape cassette into the record/reproduce apparatus and drive the tape reels 490 to rotate, the reel shafts (not shown) on the record/reproduce apparatus are passed through the reel shaft insertion holes 492a in the lower half 492 and inserted into the holes 490c formed in the lower sides of the tape reels 490; due to the resulting engagement, the pivot 490b on each tape reel 490 depresses the center portion 488a of the leaf spring 488, whereupon the two end portions 488b and 488c of the leaf spring 488 that fit into the grooves 496 in the upper half 494 contact the end portions of the respective grooves 496 in their longitudinal direction, deforming to urge the tape reels 490 toward the lower half 492.
JP 52-53205 Y discloses a reel retaining spring unit which, being indicated by 500 in FIGS. 56A and 56B, is an integral assembly of a spring body 500a and a plurality of legs 500b that extend radially from the spring body 500a (and which are three in the illustrated case). The spring units 500 each have a slider 500c at the distal end of the leg 500b and these sliders 500c are placed within slots 504 in the upper half 502 such that projections 504a in the slots 504 are brought into engagement with lugs 500d of the sliders 500c of the spring units 500; each of the sliders 500c is allowed to slide along the slot 504 until the spring body 500a of the spring unit 500 contacts a metal ball 506b fitted at the center of the reel hub 506a of each tape reel 506 and urges it toward the lower half 508.
JP 3-242889 A discloses a reel retaining spring which, being indicated by 512 in FIG. 57, consists of a plurality of radially extending legs 512a (that are four in the illustrated case) and which is mounted as an integral unit with the center of the upper surface of each tape reel 510, namely, on the upper surface of the reel hub 510a. According to the patent, the reel retaining spring 512 is made of metal or highly resilient plastic. While there is no specific disclosure of how to render the reel retaining spring 512 integral with the tape reel 510, the patent shows by illustration that the legs 512a of the reel retaining spring 512 can be secured to the upper surface of the reel hub 510a of the tape reel 510 by screwing or welding as in the prior art (see FIG. 57).
As mentioned above, the magnetic tape cassettes are made of metal or various kinds of resin. With the recent growing concern over environmental problems, increasing attention is drawn to the possibility that the increase in various kinds of wastes including those of metals, resins (plastics) and composite materials may cause adverse effects on the environment. A design consideration that is becoming important is reducing the impact on the environment by producing less wastes or developing products which, if discarded, will not cause air, water or soil pollution and hence do not become any problem in environmental conservation. To this end, it is necessary to design industrial products, in particular, magnetic tape cassettes that can be recycled at an existing plant system.
To meet this need, JP 11-273295 A discloses a design that can be applied to magnetic tape cassettes in order to facilitate assorted collection of metals and plastics. This is achieved by a mesa-shaped metallic reel retaining spring which, being indicated by 522 in FIGS. 58A, 58B and 58C, comprises a central depressing portion 522a that depresses the central area of a tape reel 520, support portions 522c at opposite ends that are detachably supported on the upper half 524, and a slope 522b that bridges the central depressing portion 522a and the support portion 522c at either end. To mount the mesa-shaped reel retaining spring 522 on the upper half 524, the support portions 522c at opposite ends of the spring 522 are passed into insertion areas 528 formed in lugs 526a at four sites on the perimeter of a transparent window member 526 in the upper half 524. The insertion areas 528 may be through-holes or may be closed at an end. The window member 526 has a weld rib 526b formed inward of the lugs 526a and on the perimeter of the side which faces the upper half 524; by melting the weld rib 526, the window member 526 can be welded to the upper half 524.
Because of this design, the tape cassette disclosed in JP 11-273295 A has the advantage that no special jig or cutting tools need be used to dislodge the metallic reel retaining spring (reel urging spring) from the upper half and collect it as metal material.
The prior art products described above have their own problems. First, the metallic or resinous reel retaining springs illustrated in FIGS. 53, 54 and 57 which are used in prior art magnetic tape cassettes are mounted on the inner surface of the upper half by securing means such as crimping, welding and screwing. Hence, when disassembling a conventional magnetic tape cassette after use and separating the components according to whether they are made of resin or metal or resinous parts are separated by resin type with a view to collecting the components by material, the reel retaining spring cannot be dislodged easily; needless to say, it cannot be removed unless the cassette case is disassembled and dislodging the reel retaining spring from the inner surface of the upper half is a complex operation that involves considerable labor and cost. This has been a factor that precludes the effort to break down the magnetic tape cassette according to material and collect and recycle the respective components in assortment.
The reel urging, metallic leaf spring 488 illustrated in FIGS. 55A and 55B is simply retained by the force of friction with the groove 496 into which it has been fitted, so it can be easily disengaged from the groove 496. On the other hand, the leaf spring 488 may potentially come out of engagement with the groove 496 during assembly. As another problem, the lateral surfaces of the leaf spring 488 contact two walls of the groove 496 in the direction of shorter side whereas the two end portions 488b and 488c contact the other two walls of the groove 496 in the direction of longer side (see FIG. 55B) and this may potentially result in chipping the wall portions of the groove 496.
The metallic spring unit 500 illustrated in FIGS. 56A and 56B is such that the slider 500c of the leg portion 500b is constricted at the lug 500d to receive the projection 504a extending from the slot 504 to come into engagement with the lug 500d. It is not very difficult to bring the two lugs out of engagement but, on the other hand, assembling the metallic spring unit 500 is a complicated work, causing various problems such as the potential breaking of the resinous projection 504a and resin chipping of the bottom of the slot 504 due to the sliding of the slider 500c. 
The metallic reel retaining spring 522 illustrated in FIGS. 58A, 58B and 58C can be easily dislodged from the upper half 524; however, if each of the insertion areas 528 has a closed end, the distal end of each support portion 522c of the reel retaining spring 522 may potentially cause resin chipping of the insertion areas 528 whereas if they are through-holes, difficulty is involved in molding operations or there is the need to form each insertion area 528 by securing two parts together and an extra step must be performed to make the lugs 526a on the inner surface of the upper half 524. What is more, the reel retaining spring 522 may be easy to separate from the upper half 524 but, on the other hand, the window member 526 which is welded to the upper half 524 cannot be easily dislodged.
These problems are by no means limited to the metallic reel retaining spring 522, they also occur in resinous reel retaining springs.
Speaking of various prior art magnetic tape cassettes including the above-described two-reel type which has a web of magnetic tape stretched between a pair of tape reels that are housed rotatably within a cassette case, if they are discarded after use, they are simply disposed of as unburnable waste in the current practice. However, as already mentioned, in order to save resources or protect the environment, it is most desirable to break down the discarded magnetic tape cassette into various parts, assort them by material and recycle the respective materials as feedstock for a second production.
In the conventional magnetic tape cassette, however, a pair of tape reels between which a web of magnetic tape is stretched are usually each composed of a lower flange integral with a reel hub around which the magnetic tape is wound and an upper flange fixed to the upper end of the reel hub, and the two flanges which are made of different materials are fastened together by ultrasonic or thermal welding. Once the upper and lower flanges are fastened together by ultrasonic or thermal welding to make a tape reel, considerable difficulty is involved in disassembling it safely and assorting the individual components by material.
The precision in assembly of the upper flange relative to the reference plane of the lower flange (which is usually its lower surface) is desirably as small as possible in order to prevent wobbling of the upper flange and keeping the magnetic tape wound in neat form and, most desirably, the precision is about 0.01 mm and less. However, the surface of the upper flange which is to be welded to the lower flange and the reference plane of the lower flange are not usually molded by a single die but molded by two dies, one fixed and the other movable, and on account of various factors including the precision in mating of dies, its thermal deformation and the pressure of molten plastic being injected, the mating position of dies is inevitably subject to change and it has been difficult to secure adequate precision in assembly of the upper flange. As a further problem, the upper flange is welded to the lower flange in a position much inward of its circumference and the wobbling of the upper flange will increase progressively from the center outward; as an inevitable result, the practically feasible precision in assembly of the upper flange has been about 0.1 mm–0.5 mm.
As already mentioned, the magnetic tape cassette is disassembled into respective components which are assorted so that they can be recycled as feedstock for a second production. In view of this, the components to be assorted are desirably made of the fewest kinds of materials and total elimination of metal from the magnetic tape cassette has been proposed. Hence, it is desired that the reel retaining spring which is conventionally made of metal and used to prevent unwanted rotation of magnetic tape should also be replaced by a plastic leaf spring. In addition, in order to ensure that the leaf spring is not an impurity that gets into the discarded upper half when it is recycled as feedstock for a second production, the retaining spring is desirably made of the same material as the upper half on which it is to be mounted.
However, the upper half which combines with the lower half to make the cassette case must have sufficiently high rigidity and strength that it can not only be loaded into or unloaded from the record/reproduce apparatus but also withstand transport. If highly rigid plastic is chosen to make the reel hub retaining spring of the same material as the upper half, the spring load will change considerably with the slightest change in thickness. Hence, in order to determine the thickness of the spring that assures an appropriate spring load for preventing unwanted rotation of magnetic tape, a lot of samples must be prepared at different thicknesses and it is necessary to check for the appropriate thickness of spring; on top of this, variations in thickness must be controlled but this adds to the complexity in manufacturing procedures.